A non-contact IC tag comprises an antenna circuit and an IC chip (chip with a built-in integrated circuit) that stores required information. A non-contact IC tag is placed at a distance, for instance stuck on an object located at a distance. Thus, the information stored in one or more non-contact IC tags are obtained through radio transmission between these non-contact IC tags and an external antenna located at a distance from them. The information acquisition using non-contact IC tags has good features that cannot be achieved by the information acquisition mechanism based on bar codes, and in particular, their use is promoted in the field of distribution of merchandise.
Some common non-contact IC tags suffer serious influence on its communication performance caused by the object that carries them. If the tag-carrying object is metal, in particular, the communication between the non-contact IC tag installed on it and the external antenna can be impeded seriously. Specifically, if a non-contact IC tag is installed on a metal member, the impedance matching between the IC chip in the non-contact IC tag and the antenna in the non-contact IC tag can deteriorate largely.
As a result, the electric power gained through the radio wave resonance in the antenna will not be supplied to the IC chip efficiently, failing to obtain electric power required to drive the IC chip. This makes impossible to achieve information transmission between the non-contact IC tag and a reader/writer located at a distance from the non-contact IC tag. This phenomenon will be particularly noticeable in cases where radio wave (microwave) is used as transmission means in combination with passive-type non-contact IC tags which do not use a battery. Various non-contact IC tags have been developed to solve this problem. Of such IC tags, well-known ones include the following.
(1) An IC tag comprising a first antenna formed on a first insulating material and a second antenna formed with a second insulating material in between, wherein the length of the second antenna is adjusted to an appropriate value to allow the IC tag to perform communication when located on a metal member (Patent Literature 1).
(2) An IC tag comprising a plastic base with a dipole antenna on one side and a metal layer on the other side wherein stripe-like portions of the metal layer extending in the direction perpendicular to the dipole antenna are removed (Patent Literature 2).
(3) An IC tag comprising a foamed resin inserted between the IC tag and a metal member carrying the IC tag so that the contact between the IC tag and the metal member is avoided to reduce the influence of the metal to make communication possible (Patent Literature 3).
(4) An IC tag comprising a magnetic material inserted between the IC tag and a metal member carrying the IC tag to decrease the influence of the metal to improve the communication (Patent Literature 4).